In JP 2003-83707A, a strain sensor is disclosed. In the strain sensor, an external force is applied to a detecting member pressed into a detecting hole of a sensor substrate (strain member) and a reaction force is applied to first and second fixing members respectively pressed into first and second fixing holes disposed at both sides of the detecting hole. First and fourth strain detecting elements are provided between the detecting hole and the first fixing hole and second and third strain detecting elements are provided between the detecting hole and the second fixing hole. The strain detecting elements are connected by a circuit pattern to structure a bridge circuit and the output from the bridge circuit is amplified by an integrated circuit provided at an upper surface of the sensor substrate to output the amplified output to an exterior portion from an external output electrode provided together with an external power electrode and an external GND electrode at an end portion of the sensor substrate.
In JP2004-268620A, an occupant load sensor, which is interposed between a floor side fixing member and a seat side fixing member for measuring a load of an occupant seated on a seat, is disclosed. This occupant load sensor is structured by a flange portion, a bolt portion, and sensors. The flange portion is mounted to the floor side fixing member contacting a surface of the floor side fixing member. The bolt portion is in contact with the flange portion and protrudes in a vertical direction to be fixed to the seat fixing member with a nut. The sensors are attached to a strain portion provided at a connection portion, which connects the flange portion to the bolt portion, and detect a load applied in an axial direction. A signal line is connected to the sensors via a terminal box.
The stain sensor disclosed in JP 2003-83707A detects the load with strain of the sensor substrate and thus the measurable range of the load is limited. Therefore, it is not possible to interpose the strain sensor between the floor side fixing member, which secures the seat to the vehicle floor, and the seat side fixing member. Also, it is necessary to enclose the entire sensor substrate in a case in order to protect the sensor substrate, the first to fourth strain detecting elements, a circuit pattern, an integrated circuit and the like.
In the occupant load sensor disclosed in JP2004-268620A, the sensors are connected to the amplifier, which is located at another position, with the signal line via the terminal box. Thus, it is not possible to amplify the output of the sensors in the vicinity of the occupant load sensor.
A need exists for an occupant load sensor for a vehicle which is not susceptible to the drawback mentioned above.